Independent normalization for γ -ray strength functions: The shape method

Abstract

The shape method, a novel approach to obtain the functional form of the γ -ray strength function (γ SF), is introduced. In connection with the Oslo method the slope of the nuclear level density (NLD) and γ SF can be obtained simultaneously even in the absence of neutron resonance spacing data. The foundation of the shape method lies in the primary γ -ray transitions which preserve information on the functional form of the γ SF. The shape method has been applied to 56 Fe, 92 Zr, and 164 Dy, which are representative cases for the variety of situations encountered in typical NLD and γ SF studies. The comparisons of results from the shape method to those from the Oslo method demonstrate that the functional form of the γ SF is retained regardless of nuclear structure details or J π values of the states fed by the primary transitions.

Comprehensive Test of the Brink-Axel Hypothesis in the Energy Region of the Pygmy Dipole Resonance

“…Finally, we test the spin independence of the present results by applying a novel approach to extract the energy dependence of the GSF in a largely model-independent way (the so-called "shape method" [67]). Here, we use the capability of the OSCAR array to resolve the decay to the ground state and to the first excited 2 þ state studying again the case of the 120 Sn isotope (regions 1 and 2 in Fig.…”

Evolution of the $γ$-ray strength function in neodymium isotopes

“…band for well-deformed nuclei and (ii) the recently developed Shape method [12]. Only 150 Nd works for the sidefeeding method, whereas the Shape method may be used for all nuclei if the final levels are known and experimentally separable.…”

“…We will now test if the above findings are consistent with the Shape method results and known (n, γ) data. The Shape method [12] relies on measuring the number of counts N D in a diagonal D of the primary matrix defined by E i = E γ + E f for a fixed value of E f . Such a diagonal is revealed in Fig.…”

“…The obtained strength function f (E γ ) has in principle the correct functional form, but the absolute normalization is arbitrary and must be determined by other means. More details of the Shape method are given by Wiedeking et al [12].…”

“…In the present work, we have measured the γSFs of 142,144−151 Nd using particle-γ coincidences from light-ion reactions on stable neodymium targets. The data were analyzed within the framework of the Oslo method [9][10][11] and the recently developed Shape method [12]. By also exploiting experimental results from other measurements, the evolution of the γSF in the energy region of E γ ≈ 0 − 17 MeV and the interplay between its various components are discussed as function of deformation and mass number.…”